In the olfactory system, olfactory receptor neurons (ORNs) distributed widely in the sensory epithelium converge with great precision on specific points in the brain to form an invariant map of odorant representation. The molecular mechanism that governs this phenomenon is not fully understood. Experiments presented in this application will address this question by using the zebrafish to develop a transgenic system which will allow in vivo observation of olfactory development. Subsets of olfactory receptor neurons will be tagged with GFP expression in an odorant receptor-specific manner. The development of these tagged neurons will be characterized in stable transgenic zebrafish embryos and the overall development of the zebrafish olfactory system will be elucidated. Through genetic manipulation and in vivo imaging, I will determine the nature of the olfactory sensory map in the zebrafish, the role of the olfactory receptor in the targeting of ORNs, and the possible role of pioneer neurons in establishing the spatial map. Elucidating the molecular mechanisms underlying olfactory map formation in zebrafish will pave the way for detailed genetic analysis of axon pathfinding and coding in the olfactory system.